Cortisol
Cortisol is a catabolic hormone primarily responsible for mobilization of energy stores in response to a stress stimulus. The greater the stressor, the greater the cortisol catabolic effect. In order to achieve an anabolic effect, cortisol must be minimized in relation to the anabolic hormone. Therefore a measure such as comparing cortisol levels to
testosterone levels (free
testosterone: cortisol ratio (FTCR)) may give an accurate level of the anabolic status concerning the interaction of those two hormones (Vervoon 1992). It is important to note that cortisol tends to have proportional acrophase diurnal secretation levels proportional to testosterone (Van Cauter 1990). Another example for determining anabolic status may be determining the
GH or GF's to cortisol ratio after exercise. Anabolic status is more important after exercise than during exercise since it is after exercise that tissue recovery and growth take place.
In other words, it is important to consider the effects of cortisol when considering the anabolic "portrait" or "profile" of an individual. For example, a situation in which testosterone levels may be high and
GH pulses are large and frequent may suggest an anabolic condition. However, in this case cortisol may also be consistently high which would negate the effect of the two anabolic hormones and might suggest that
GH is high due to a large stress response.
Application of the Discussed Hormones, Growth Factors, and Biological Rhythms on Exercise Recovery and Tissue Growth
In general, a situation which encourages tissue growth and protein synthesis within the body is beneficial to exercise recovery. Therefore these two situations (recovery and tissue growth) will be used synonymously throughout this section.
Perhaps the most important factor in governing recovery and tissue growth is to establish a set daily pattern of meals, exercise, and sleep and follow this pattern as closely as possible. This will ensure regulated and optimal levels of anabolic hormones and growth factors as well as a decrease in stress, subsequently decreasing cortisol. Each factor pertinent to the diurnal and ultradian cycles will be discussed in more detail in the following paragraphs.
(1) Sleep - Since
GH is an anabolic hormone, length and quality of sleep is essential for maximal tissue regeneration, and tissue growth. As previously, discussed
GH levels peak during the stages of deep sleep (stages 3 and 4) and seem to follow an ultradian pattern throughout the night, generally decreasing in amplitude throughout sleep (Van Cauter 1990). Additionally,
GH release positively affects testosterone secretion which both interact with necessary growth factors that also have a powerful effect on tissue growth and recovery. Alterations in the sleep-wake cycle can negatively affect testosterone levels. Therefore, an established daily pattern of sleep times is important.
(2) Daily meals - Nutrient abundance is necessary for an anabolic state while nutrient deficiency will result in a catabolic state concerning tissue growth. Meals should be eaten throughout the day at regular intervals. The pre-exercise meal should be low in fat in order not to suppress
GH release by inhibiting somatostatin release from the pancreas. A meal high in glucose should also be avoided as this can inhibit
GH.
The evening meal should be eaten well ahead of sleep times and be low in fat, in order that the amplitude of ultradian patterns of
GH are not suppressed. It appears that a lower blood glucose level stimulates
GH release as well therefore it is important to allow enough time to allow insulin to bring blood glucose down and stabilize it.
Regarding the circadian effect of insulin, the majority of meals should be eaten during the day and early evening in order to maximize the effect of lower blood glucose levels and its positive effect on allowing full expression of
GH amplitude.
As mentioned above, high
growth hormone levels stimulate necessary growth factors for recovery and tissue growth. This is why optimally high levels of
GH during recovery are important for tissue growth.
(3) Exercise - Exercise is the main external factor that causes tissue growth and subsequent adaption to the stimulus. Resistance exercise emphasizing volume tends to be the greatest stimulus for tissue growth through increases in pulses and amplitude of
GH, growth factors, and testosterone. Increasing frequency of brief and intense training sessions may bring about increased growth through increased number of pulses of
GH.
Intensity must be given adequate attention as too much will increase cortisol levels and destroy the anabolic condition. Too little intensity will not bring about necessary rises in
GH pulse frequency and amplitude, testosterone levels, and other necessary metabolic changes.
When endurance is the goal of the athlete, attention must be paid concerning the duration of exercise. Too long a duration will increase cortisol ratios and negatively affect recovery; too short a duration will not provide adequate stimulus to the energy systems to improve performance.
GH appears to regulate mobilization of energy stores when it comes to endurance training more so than causing musculoskeletal hypertrophy. Testosterone does not seem to be a factor in improving endurance performance as testosterone typically decreases with long term endurance training.
Conclusion
As previously discussed, diurnal, ultradian, and circadian rhythms tend to govern the secretion patterns of hormones. Since few hormonal responses are truly circadian in nature, several factors such as sleep-wake cycles, nutrition, meal timing, exercise, other hormones, and stress can alter diurnal rhythm patterns. It is precisely for this reason that competitive and recreational athletes and their coaches should be aware of these cycles and related hormonal interactions as well as the individual hormonal effects of exercise.
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